The present invention relates to the construction of multi-story buildings, and more particularly to an improved composite structural framing system and associated method of construction wherein concrete plank sections are assembled and grouted about a specially adapted open web dissymmetric steel beam having a plurality of openings made through the web of the beam along the length thereof to improve grout flow through and about the beam so that the resulting concrete encasement of the beam develops greater composite action and structural integrity in the system.
In the field of building construction, particularly in those buildings of multiple stories, the framing system provides the essential load bearing element that characterizes and determines the load carrying capacity and structural integrity of the building. Designed to comply with standard building code requirements, the framing systems of modern multi-story buildings are generally made of heavy, fire-resistive materials, such as structural steel and concrete. Typically consisting of a plurality of vertical steel columns and horizontal steel beams extending between and connected to each column, the standard framing system further includes floors of reinforced concrete that may be precast or cast-in place supported by and between the horizontal beams on each level. While each framing system must be designed to safely carry all of the anticipated vertical loads affecting the building and provide stabilization against lateral loads caused by wind or other horizontal forces, it is important that the system be easy to assemble and cost-effective as well in order to afford its use in modern construction projects.
In recent years, revisions to the national and international building code standards, particularly those model provisions of the Building Officials and Code Administrators International, Inc. (BOCA), have increased lateral load requirements for seismic design criteria, especially affecting multi-story building construction. As a result, the framing systems of most prospective multi-story building structures will be required to resist lateral loads greater than those able to be accommodated by much of the existing structural framework incorporated into building construction over the last few decades. Because of the increased seismic design criteria and the continuing pressure of minimizing construction costs, new design alternatives for structural framing systems have been developed in order to meet all of the current loading requirements imposed upon modern multi-story buildings in an economical and cost-effective manner.
One recent design alternative for a structural framing system is described in U.S. Pat. No. 5,704,181 wherein a dissymmetric steel beam having a compressed, block-like top flange, a flattened bottom flange, and a continuous solid web integrally extending therebetween is adapted to be horizontally disposed between adjacent vertical steel columns that are erected upon conventional foundations. Standard hollow core sections of precast, prestressed concrete plank are then installed along either side of the dissymmetric beam supported upon the bottom flange and together assembled so that the beam is disposed centrally between facing edges of the plank sections all in substantially the same horizontal plane. Grouting of the assembled beam and plank sections then provides encasement of the beam, interlocking the beam and plank sections and developing a composite action that enhances the loadbearing capacity of the system. While the framing system of the aforementioned patent has performed satisfactorily and produced increased loadbearing results in testing that are indicative of the development of composite action between the steel beam and the concrete plank, further testing has indicated a need to guarantee a more homogeneous and uniform bond between the structural steel and the precast concrete in order to ensure the maintenance of the interlocking effect and the composite action initially developed by the aforedescribed framing system.
Accordingly, it is a general purpose and object of the present invention to provide an improved structural framing system and associated method of construction that increases the structural integrity and load carrying characteristics of multi-story buildings.
A further object of the present invention is to provide a structural framing system and method of constructing same that provides a more effective and economical means for supporting the loading requirements of modern-day building structures, particularly those having multiple stories, than those structural framing systems heretofore developed.
A more specific object of the present invention is to provide an improved composite assembly of structural elements in a framing system for multi-story construction that is capable of handling all the loading requirements now specified under applicable building codes, including those lateral load requirements associated with potential seismic activity, within a minimum building elevation, and adapted to better maintain its composite strength and structural integrity over the useful life of the construction.
A still further object of the present invention is to provide a safe and effective structural framing system that may be assembled and implemented using relatively standard construction materials and equipment.
Briefly, these and other objects of the present invention are accomplished by an improved structural framing system and associated method of construction wherein an open web dissymmetric steel beam fabricated having a plurality of trapezoidal openings formed along the web thereof between a narrowed, thickened top flange and a widened bottom flange is horizontally disposed and supported between adjacent vertical columns erected on conventional foundations. The dissymmetric beam is preferably fabricated from a standard rolled, wide flange beam split longitudinally according to a specific cutting pattern to produce substantially identical open web beam sections having a single wide flange. A flat bar plate is then welded along the open web beam section to provide the top flange and thereby produce the dissymmetric beam for use in the present system. Standard hollow core sections of precast concrete plank are assembled together perpendicularly to the open web dissymmetric beam and supported upon the bottom flange on either side thereof so that the open web of the beam is centrally disposed between end surfaces of the plank sections in substantially the same horizontal plane. A high-strength grout mixture applied to the assembled beam and plank sections is made to flow completely through the web openings in a circulatory manner thereby creating a substantially monolithic concrete encasement around the dissymmetric beam that improves the resulting composite action and mechanical interlock between the steel beam and concrete plank and prevents loss of strength due to separation of the grout from either side of the beam.
For a better understanding of these and other aspects of the present invention, reference may be made to the following detailed description taken in conjunction with the accompanying drawing in which like reference numerals designate like parts throughout the figures thereof.